A field experiment was conducted to quantify the carbohydrate distribution in perennial (Lolium perenne L.) and Italian ryegrass (Lolium multiflorum L.) seed crops from anthesis to harvest. To do this, first year crops of diploid perennial ryegrass (‘Samson’) and a diploid Italian ryegrass cultivar (‘Progrow’) were sown on 14th May and 16th September 2015. A subsequent application of Moddus® (a.i. 250 g/l Trinexapac ethyl) plant growth regulator at three rates (0, 1,600 and 3,200 ml/ha) was applied at Zakoks growth stage 32.
Moddus® increased perennial and Italian ryegrass seed yield by approximately 29% from 1,600 ml/ha (1,651 kg/ha) to 3,200 ml/ha (2,134 kg/ha), with similar yields between 0 ml/ha (1,296 kg/ha) and 1,600 ml/ha. The seed yield increase in perennial and Italian ryegrass was achieved through increased number of seed produced per spikelets. The vegetative stem length in perennial and Italian ryegrass was reduced from 62 cm to 41 cm by application of 1,600 ml/ha of Moddus® and further reduced to 36 cm with 3,200 ml/ha.
The perennial ryegrass’s stem component dry weight and water soluble carbohydrate (WSC) concentration were constant from anthesis through untill harvest. Despite Moddus® reducing the stem length and its storage capacity a large amount of WSC remained in the stem components. Perennial ryegrass had the capacity to fill and improve seed yield accumulating WSC simultaneously and converting this into starch up to harvest at 37 days after anthesis (DAA) with little or no remobilisation of WSC in the stem.
Moddus® decreased Italian ryegrass’s stem components dry weight by 37% and WSC by 42% . The effect of Moddus® suggests the source and sink relationship between the stem and developing seed has been modified.The Italian ryegrass seed dry weight increased up to 7 DAA and declined until harvest with WSC and starch illustrating a similar pattern. When maximum seed weight, WSC and starch was achieved the stem component begun to decline. This demonstrates that Italian ryegrass stem may play a role in seed filling under conditions of limited assimilate supply with stem assimilate reserves remobilised to the developing seed.
Moddus® reduced overall lodging at the highest rate of 3,200 ml/ha and delayed the onset of lodging at the lower rate. Lodging progressed more quickly and had a greater effect on perennial ryegrass than Italian ryegrass. Lodging reduced perennial ryegrass seed yield with less WSC in the seed of control plants of 0 ml/ha (49.91 mg) compared to the highest Moddus® treatment of 3,200 ml/ha (59.63 mg). Italian ryegrass showed similar seed WSC between the control (88.6 mg) and the two Moddus® treatments of 1,600 ml/ha (94 mg) and 3,200 ml/ha (85.5 mg). This showed the degree which two ryegrass species seed sinks can compete for available assimilates. The relative lower seed depression in lodged Italian ryegrass compared to the perennial indicates a higher compensation potential. The Italian showed the ability to partition more assimilate reserves from the stem and…
Advisors/Committee Members: Gash, Alan.

First year crops of three diploid perennial ryegrass (Lolium perenne L.) cultivars, ‘Meridian’, ‘Bronsyn’ and ‘Grasslands Impact’, that contain the AR1 endophyte, were sown on 1 April and 14 May 2008. A subsequent application of Moddus (a.i. 250 g/l Trinexapac ethyl) plant growth regulator at three rates was used to examine the relationship between seed and stem dry weight in relation to thermal time.
Seed filling of ‘Meridian’, ‘Bronsyn’ and ‘Grasslands Impact’ followed a sigmoidal growth pattern. The lag phase was 150 growing degree days (°C days) and the duration of the linear period constant at 294 °C days. The application of Moddus increased seed yield by approximately 26% for each 800 ml/ha applied from 1715 (0 mlha) to 2195 (800 ml/ha) and 2722 kg/ha (1600 ml/ha). The time to 95% of final seed weight was constant between treatments at 443 °C days. Seed yield increase from Moddus was achieved by increased rate of seed filling per seed head, 0.24 mg/°C days/head, which increased the number of seeds/m².
For all cultivars, 1600 ml/ha of Moddus produced the highest seed yield and the shortest total stem length. There was a 0.15 m reduction in length between 0 and 1600 ml/ha of Moddus with all internodes shortened, including the seed head length. Stem dry weight increased to a maximum at between 310 and 400 °C days following anthesis. Thus, stems competed with growing seeds from anthesis, throughout the lag phase until approximately 75% of final seed weight. When seed demand for assimilate was low, lag phase and early seed growth, the stem was a competing sink. As seeds developed their sink capacity increased, thus drawing assimilate from the stem. At harvest, stems were 25% heavier than at athesis which suggests they were a net sink for assimilate post anthesis and that there was further assimilates available for seed production.
Moddus also decreased absolute lodging at harvest where stems were horizontal when no Moddus was applied compared with stems leaning on a 45 ° angle for 800 ml/ha and upright for 1600 ml/ha. Moddus increased the harvest index (HI) of plots, 13.5 – 19.8%, and individual stems, 20 – 40%, primarly through an increase in seed mass/ha while straw mass remained constant for ‘Meridian’ and ‘Bronsyn’. In ‘Grasslands Impact’ the increase in HI was limited through an associated increase in straw DM when Moddus was applied. The change in harvest index per day (dHI/dt) on main stems was linear, which suggests this could be a useful method for incorporation into crop simulation models. The dHI/dt was influenced by treatments which influenced lodging.
Competition for assimilate between stems and growing seeds was a major factor limiting the seed yield. This has implications for plant breeders and seed producers where both should aim to reduce stem length which is likely to increase the rate of seed filling. There was a clear advantage to applying Moddus at 1600 ml/ha for all cultivars which highlighted the advantage of breeding for a shorter stem.

The use of nitrogen in the culture of the wheat seeks the increase of the productivity.However, it also increases the probability of occurrence of the lodgnign. That can be avoided with the application of growth regulators. In that sense, he took place a field experiment, in the city of Castro, PR, seeking to evaluate the effects of the application of the trinexapac-ethyil in different times and of doses of nitrogen on wheat, cultivars (VANTE and BRS 77). The experimental field was…